ACTIVITIES AND STABILITIES OF REDOX MOLECULAR-SIEVE CATALYSTS IN LIQUID-PHASE OXIDATIONS - A REVIEW

The use of redox molecular sieves as heterogeneous catalysts for liqui d phase oxidations with H2O2 and alkyl. hydroperoxides is reviewed. Em phasis is placed on titanium- and chromium-substituted molecular sieve s as examples of catalysts operating via peroxometal and oxometal path ways, respectively. Various titanium-substituted molecular sieves were shown to be stable, heterogeneous catalysts for, e.g., olefin epoxida tion, but the remarkable activity of the progenitor of this family of catalysts, titanium-silicalite (TS-1), has not been equalled. The cata lytic activity of chromium-substituted molecular sieves was shown to b e entirely due to small amounts of homogeneous chromium species leache d from the catalyst during reaction. The catalytic activities and stab ilities of other materials, including zirconium-substituted hexagonal mesoporous silicas and a vanadium bipyridyl complex encapsulated in ze olite Y, were also tested. They were either unstable (vanadium) toward s leaching or showed low activity (zirconium). Attempts to incorporate molybdenum in silicalite were unsuccessful and previously reported ac tivity was shown to be due to the blank reaction. A review with 64 ref erences.